This application claims priority to an application entitled xe2x80x9cA Ribbon Optical Cable with a Loose Tubexe2x80x9d filed in the Korean Industrial Property Office on Aug. 28, 2001 and assigned Serial No. 2001-51943, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to ribbon optical cables. More particularly, the present invention relates to a ribbon optical cable with a loose tube.
2. Description of the Related Art
In the art, a ribbon optical cable is defined as an optical cable having a ribbon optical fiber as the transmission medium for an optical signal. The ribbon optical fiber is a congregated multifiber cable that is arrayed in parallel. In order to manufacture the ribbon optical fiber, the multifiber cable is first congregated in parallel, and subsequently, the optical fiber is coated with an ultraviolet curable resin. After the coating, the cable is exposed to unltraviolet to cure the resin and prepare the ribbon optical fiber.
In addition, the ribbon optical fiber can be manufactured with a matrix structure by laying a plurality of the ribbon optical fibers described above. Since the multifiber cable is congregated to make the ribbon optical fiber, the density of the optical fiber in a limited space is relatively very high. Considering that the most conduct lines available today are already paved with a number of optical cables, and that a new paving space in the conduct line is seriously deficient, the high-density ribbon optical cable, if it can be implemented, will be one of the best options people have right now. In fact, there have been some attempts to diminish the outer diameter of the optical cable in order to pave more optical fibers in that narrow conduct line, increasing the packing density of the optical fibers.
FIG. 1 is a front cross sectional view showing a loose tube paved with a ribbon optical fiber bundle in the prior art, and FIG. 2 is a side cross sectional view showing the loose tube as taken along line A-Axe2x80x2 of FIG. 1. With reference to FIG. 1, the loose tube ribbon optical cable includes: a plurality of optical fibers 120 that coat multifiber cables 110 arrayed in parallel, ribbon optical fiber bundle 130 that are prepared by layering the plural ribbon optical fibers one at a time in order, a loose tube 150 that is paved with the ribbon optical fiber bundle 130, and a jelly 140 that packs the empty space inside of the loose tube 150.
As shown FIG. 2, the ribbon optical fiber bundle 130 is smoothly bent, so as not be arranged in a straight line, along the longitudinal direction of the loose tube 150. The reason that the ribbon optical bundle 130 is bent is because the bundle grows longer than the loose tube 150. In addition, for the purpose of improving a lay ratio, the ribbon optical fiber bundle 130 in the loose tube 150 can be arranged in spiral lengths as well.
Again referring to FIGS. 1 and 2, the four edges (C, D, E and F) of the ribbon optical fiber bundle 130 are adhered closely to the inner wall of the loose tube 150, so the edges (C, D, E and F) of the ribbon optical fiber bundle 130 are subjected to a compressive force. This compressive force, on the other hand, is proportional to the lay ratio of the ribbon optical fiber bundle 130, while inversely proportional to a clearance inside of the loose tube 150. Unfortunately, such compressive force can cause microbending on the surface of the optical fiber comprising the ribbon optical fiber bundle 130, or even can be caused by flaws on the surface optical fiber. Further, the microbending is a main factor in decreasing optical signals forwarding to the optical fiber 110.
Although the microbending problem might be overcome by extending the diameter of the loose tube 150, this approach has been considered unworkable because the diameter of the ribbon optical fiber bundle for paving the loose tube 150 with the extended diameter becomes consequently enlarged as well.
It is, therefore, an object of the present invention to provide a loose tube ribbon optical cable with a smallest diameter to prevent the microbending of edges of a ribbon optical fiber bundle.
To achieve the above object, there is provided a loose tube ribbon optical cable, which includes at least one reinforced ribbon optical fiber bundle that includes a multifiber cable arrayed in parallel, a ribbon optical fiber bundle formed of multi-layered ribbon optical fibers for coating the multifiber cable, and a pair of reinforcing layers with both edges bent towards the outer ribbon optical fiber bundle, being formed on the outside of the bundle; at least one loose tube packed with the reinforced ribbon optical fiber bundle; and an outer coating disposed in a peripheral of the ribbon optical cable, enclosing the loose tube(s).